The present invention relates to a wellhead isolation tool (xe2x80x9cWITxe2x80x9d) and, more specifically, to such a tool which locates the fluid control and connection devices at the lower end of the WIT.
A WIT is typically used in an oil or gas well to protect the internal surfaces of the wellhead assembly that is installed at the top of the well bore from corrosive or erosive materials during stimulation of the well. The WIT is normally mounted on the top of the wellhead assembly and comprises a tubular mandrel which is inserted through the wellhead assembly and sealed to the production tubing string. The well stimulation fluid is then pumped through the mandrel and into the production tubing string. Means, such as one or more hydraulic cylinders, are usually provided to raise and lower the mandrel through the wellhead assembly. Because of the large stroke required to do this, the WIT is usually quite tallxe2x80x94at least as tall as the wellhead assembly. In previous WIT designs, the mandrel extends beyond the top of the hydraulic cylinders and the stimulation fluid is injected into the top end of the mandrel. To make the necessary connections, workers have to access the top of the WIT, which requires the construction of platforms, ladders and the like. This not only increases costs, but also creates a safety concern.
In accordance with the present invention, these and other limitations in the prior art are overcome by providing a wellhead isolation tool for use with a wellhead assembly from which a tubing string is suspended, the wellhead isolation tool comprising a tubular mandrel which includes an axial passage that extends therethrough and a lower end that is adapted to engage the tubing string, a pumping head which is connected over the wellhead assembly and which includes an internal chamber that is in fluid communication with the axial passage and a port that extends through the pumping head to the chamber, and an actuator assembly which is connected over the pumping head and which functions to move the mandrel axially through the pumping head and into engagement with the tubing string. In this manner, when the mandrel is engaged with the tubing string, fluid may be communicated through the port, the chamber and the mandrel and into the tubing string.
In accordance with a preferred embodiment of the invention, the wellhead isolation tool also comprises a sleeve which is connected between the actuator assembly and the mandrel and which is positioned at least partially within the chamber when the mandrel is engaged with the tubing string. The sleeve comprises an axial bore that communicates with the axial passage in the mandrel and at least one generally radial bore that communicates between the chamber and the axial bore.
In addition, the wellhead isolation tool preferably includes a generally cylindrical diffusion element which is positioned within the chamber. The diffusion element includes an outer diameter surface, an inner diameter surface which surrounds at least a portion of the sleeve when the mandrel is engaged with the tubing string, and a plurality of holes which extend generally radially between the inner and outer diameter surfaces.
Thus, the present invention allows the well stimulation fluid to be injected from the side of the pumping head, which is located between the wellhead assembly and the actuator assembly. Consequently, all the control, injection and lockdown functions are located in one convenient area at the lower end of the WIT. Therefore, no need exists to access the top of the WIT, which reduces costs and safety concerns. In addition, the diffusion element disperses the flow of the incoming fluid and thus prevents the fluid from impinging on isolated spots within the sleeve. Therefore, the diffusion element prevents the fluid from unduly eroding the sleeve.
These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings.